Antireflective silicon-containing compositions as hardmask layer

ABSTRACT

Antireflective compositions characterized by the presence of an SiO-containing polymer having pendant chromophore moieties are useful antireflective coating/hardmask compositions in lithographic processes. These compositions provide outstanding optical, mechanical and etch selectivity properties while being applicable using spin-on application techniques. The compositions are especially useful in lithographic processes used to configure underlying material layers on a substrate, especially metal or semiconductor layers.

BACKGROUND OF THE INVENTION

In the microelectronics industry as well as in other industriesinvolving construction of microscopic structures (e.g. micromachines,magnetoresistive heads, etc.), there is a continued desire to reduce thesize of structural features. In the microelectronics industry, thedesire is to reduce the size of microelectronic devices and/or toprovide greater amount of circuitry for a given chip size.

Effective lithographic techniques are essential to achieving reductionof feature sizes. Lithography impacts the manufacture of microscopicstructures not only in terms of directly imaging patterns on the desiredsubstrate, but also in terms of making masks typically used in suchimaging. Typical lithographic processes involve formation of a patternedresist layer by patternwise exposing the radiation-sensitive resist toan imaging radiation. The image is subsequently developed by contactingthe exposed resist layer with a material (typically an aqueous alkalinedeveloper) to selectively remove portions of the resist layer to revealthe desired pattern. The pattern is subsequently transferred to anunderlying material by etching the material in openings of the patternedresist layer. After the transfer is complete, the remaining resist layeris then removed.

For some lithographic imaging processes, the resist used does notprovide sufficient resistance to subsequent etching steps to enableeffective transfer of the desired pattern to a layer underlying theresist. In many instances (e.g., where an ultrathin resist layer isdesired, where the underlying material to be etched is thick, where asubstantial etching depth is required, and/or where it is desired to usecertain etchants for a given underlying material), a so-called hardmasklayer is used intermediate between the resist layer and the underlyingmaterial to be patterned by transfer from the patterned resist. Thehardmask layer receives the pattern from the patterned resist layer andshould be able withstand the etching processes needed to transfer thepattern to the underlying material.

Also, where the underlying material layer is excessively reflective ofthe imaging radiation used to pattern the resist layer, typically a thinantireflective coating may be applied between the underlying layer andthe resist layer. In some instances, the antireflection and hardmaskfunctions may be served by the same material.

While many hardmask and antireflective coating materials exist in theprior art, there is a continued desire for improved compositions. Manyof the prior art materials are difficult to apply to the substrate,e.g., they may require use of chemical or physical vapor deposition,and/or high temperature baking. It would be desirable to haveantireflective coating/hardmask compositions which could be applied byspin-coating techniques without need for a high temperature bake.Additionally, it is desirable to have hardmask compositions which can beeasily etched selective to the overlying photoresist while beingresistant to the etch process needed to pattern the underlying layer,especially where the underlying layer is a metal layer.

SUMMARY OF THE INVENTION

The invention encompasses novel antireflective coating/hardmaskcompositions which are useful in lithographic processes. Thesecompositions provide outstanding optical, mechanical and etchselectivity properties while being applicable using spin-on applicationtechniques. The antireflective compositions are characterized by thepresence of an SiO containing polymer having pendant chromophoremoieties. The invention also encompasses lithographic structurescontaining the antireflective coating/hardmask composition of theinvention, methods of making such lithographic structures and methods ofusing such lithographic structures to pattern underlying material layerson a substrate.

In one aspect, the invention encompasses a composition suitable forformation of a spin-on antireflective layer, the composition comprising:

(a) a polymer containing SiO moieties and chromophore moieties,

(b) a crosslinking component, and

(c) an acid generator.

The SiO moieties are preferably selected from the group consisting ofsiloxane moieties and silsesquioxane moieties. The SiO moieties arepreferably in a backbone portion of the polymer. The SiO-containingpolymer also preferably contains a plurality of reactive sitesdistributed along the polymer for reaction with the crosslinkingcomponent. The acid generator is preferably a thermally activated acidgenerator.

In another aspect, the invention encompasses a lithographic structure ona substrate, the structure comprising:

(a) an antireflective layer comprising a crosslinked polymer containingSiO moieties and chromophore moieties, and

(b) a radiation-sensitive imaging layer over the antireflective layer.

In another aspect, the invention encompasses method of forming apatterned material feature on a substrate, the method comprising:

(a) providing a material layer on a substrate,

(b) forming an antireflective layer over the material layer, theantireflective layer comprising a crosslinked polymer containing SiOmoieties and chromophore moieties,

(c) forming a radiation-sensitive imaging layer over the antireflectivelayer,

(d) patternwise exposing the imaging layer to radiation thereby creatinga pattern of radiation-exposed regions in the imaging layer,

(e) selectively removing portions of the imaging layer and theantireflective layer to expose portions of the material layer, and

(f) etching the exposed portions of the material layer, thereby formingthe patterned material feature.

The material to be patterned is preferably a conductive, semiconductive,magnetic or insulative material, more preferably a metal. The SiOmoieties are preferably in a backbone portion of the polymer. TheSiO-containing polymer also preferably contains a plurality of reactivesites distributed along the polymer for reaction with the crosslinkingcomponent.

The invention also encompasses methods of making lithographicstructures. These and other aspects of the invention are discussed infurther detail below.

DETAILED DESCRIPTION OF THE INVENTION

The invention encompasses novel antireflective coating/hardmaskcompositions which are useful in lithographic processes. Theseantireflective compositions are characterized by the presence of anSiO-containing polymer having pendant chromophore moieties. Theinvention also encompasses lithographic structures containing theantireflective coating/hardmask composition of the invention, methods ofmaking such lithographic structures and methods of using suchlithographic structures to pattern underlying material layers on asubstrate.

The antireflective compositions of the invention generally comprise:

(a) a polymer containing SiO moieties and chromophore moieties,

(b) a crosslinking component, and

(c) an acid generator.

The polymer containing SiO moieties may be a polymer containing SiOmoieties in the polymer backbone and/or in pendant groups. Preferably,the polymer contains SiO moieties in its backbone. The polymer ispreferably an organosiloxane, more preferably organosilsesquioxane. Thepolymer should have solution and film-forming characteristics conduciveto forming a layer by conventional spin-coating. In addition to thechromophore moieties discussed below, the SiO-containing polymer alsopreferably contains a plurality of reactive sites distributed along thepolymer for reaction with the crosslinking component.

Examples of suitable polymers include polymers having the silsesquioxane(ladder or network) structure. Such polymers preferably contain monomershaving structures (I) and (II) below:

where R₁ comprises a chromophore and R₂ comprises a reactive site forreaction with the crosslinking component.

Alternatively, general linear organosiloxane polymers containingmonomers (III) and (IV) can be used:

where R₁ and R₂ are as described above. In some cases, the polymercontain various combinations of monomers (I)-(IV) such that the averagestructure for R₁-containing monomers may be represented as structure (V)below and the average structure for R₂-containing monomers may berepresented by structure (VI) below:

where x is from about 1 to about 1.5. In theory, x may be greater than1.5, however, such composition generally do not possess characteristicssuitable for spin-coating processes (e.g., they form undesirable gel orprecipitate phases).

Generally, silsesquioxane polymers are preferred on the basis ofsuperior etch resistance. If the ordinary organosiloxane polymers areused (e.g., monomers of structures (III) and (IV)), then preferably, thedegree of crosslinking is increased compared to formulations based onsilsesquioxanes.

The chromophore-containing groups R₁ may contain any suitablechromophore which (i) can be grafted onto the SiO-containing polymer(ii) has suitable radiation absorption characteristics, and (iii) doesnot adversely affect the performance of the layer or any overlyingphotoresist layers. Preferred chromophore moieties include chrysenes,pyrenes, fluoranthrenes, anthrones, benzophenones, thioxanthones, andanthracenes. Anthracene derivatives, such as those described in U.S.Pat. No. 4,371,605 may also be used; the disclosure of this patent isincorporated herein by reference. 9-anthracene methanol is a preferredchromophore. The chromophore moiety preferably does not containnitrogen, except for possibly deactivated amino nitrogen such as inphenol thiazine.

The chromophore moieties may be chemically attached to the SiOcontaining polymer by acid-catalyzed O-alkylation or C-alkylation suchas by Friedel-Crafts alkylation. Alternatively, the chromophore moietymay be attached by an esterification mechanism. A preferred acid forFriedel-Crafts catalysis is HCl. Preferably, about 15 to 40% of thefunctional groups (R₁) contain chromophore moieties. In some instances,it may be possible to bond the chromophore to the monomer beforeformation of the SiO-containing polymer, however this is generally notpreferred. The site for attachment of the chromophore is preferably anaromatic group such as a hydroxybenzyl or hydroxymethylbenzyl group.Alternatively, the chromophore may be attached by reaction with othermoieties such as cyclohexanol or other alcohols. The reaction to attachthe chromophore is preferably an esterification of the alcoholic OHgroup.

R₂ comprises a reactive site for reaction with the crosslinkingcomponent. Preferred reactive moieties contained in R₂ are alcohols,more preferably aromatic alcohols (e.g., hydroxybenzyl, phenol,hydroxymethylbenzyl, etc.) or cycloaliphatic alcohols (e.g.,cyclohexanoyl). Alternatively, non-cyclic alcohols such as fluorocarbonalcohols, aliphatic alcohols, amino groups, vinyl ethers, and epoxidesmay be used.

Preferably, the SiO-containing polymer (before attachment of thechromophore) is poly(4-hydroxybenzylsilsesquioxane). Examples of othersilsesquioxane polymers of the invention include:poly(p-hydroxyphenylethylsilsesquioxane),poly(p-hydroxyphenylethylsilsesquioxane-co-p-hydroxy-α-methylbenzylsilsesquioxane),poly(p-hydroxyphenylethylsilsesquioxane-co-methoxybenzylsilsesquioxane),poly(p-hydroxyphenylethylsilsesquioxane-co-t-butylsilsesquioxane),poly(p-hydroxyphenylethylsilsesquioxane-co-cyclohexylsilsesquioxane),poly(p-hydroxyphenylethylsilsesquioxane-co-phenylsilsesquioxane),poly(p-hydroxyphenylethylsilsesquioxane-co-bicycloheptylsilsesquioxane),poly(p-hydroxy-α-methylbenzylsilsesquioxane),poly(p-hydroxy-α-methylbenzylsilsesquioxane-co-p-hydroxybenzylsilsesquioxane),poly(p-hydroxy-α-methylbenzylsilsesquioxane-co-methoxybenzylsilsesquioxane),poly(p-hydroxy-α-methylbenzylsilsesquioxane-co-t-butylsilsesquioxane),poly(p-hydroxy-α-methylbenzylsilsesquioxane-co-cyclohexylsilsesquioxane),poly(p-hydroxy-α-methylbenzylsilsesquioxane-co-phenylsilsesquioxane),poly(p-hydroxy-α-methylbenzylsilsesquioxane-co-bicycloheptylsilsesquioxane),andpoly(p-hydroxybenzylsilsesquioxane-co-p-hydroxyphenylethylsilsesquioxane).The polyorganosiloxane polymers described in US Pat. No. 5,100,503 aregenerally not useful for creating low temperature bake compositions dueto their very low reactivity with crosslinking components; thedisclosure of this patent is incorporated herein by reference.

The SiO-containing polymers of the invention preferably have a weightaverage molecular weight, before reaction with the crosslinkingcomponent, of at least about 1000, more preferably a weight averagemolecular weight of about 1000-10000.

The crosslinking component is preferably a crosslinker that can bereacted with the SiO containing polymer in a manner which is catalyzedby generated acid and/or by heating. Generally, the crosslinkingcomponent used in the antireflective compositions of the invention maybe any suitable crosslinking agent known in the negative photoresist artwhich is otherwise compatible with the other selected components of thecomposition. The crosslinking agents preferably act to crosslink thepolymer component in the presence of a generated acid. Preferredcrosslinking agents are glycoluril compounds such as tetramethoxymethylglycoluril, methylpropyltetramethoxymethyl glycoluril, andmethylphenyltetramethoxymethyl glycoluril, available under thePOWDERLINK trademark from American Cyanamid Company. Other possiblecrosslinking agents include: 2,6-bis(hydroxymethyl)-p-cresol, compoundshaving the following structures:

including their analogs and derivatives, such as those found in JapaneseLaid-Open Patent Application (Kokai) No. 1-293339, as well as etherifiedamino resins, for example methylated or butylated melamine resins(N-methoxymethyl- or N-butoxymethyl-melamine respectively) ormethylated/butylated glycolurils, for example as can be found inCanadian Patent No. 1 204 547. Other crosslinking agents such asbis-epoxies or bis-phenols (e.g., bisphenol-A) may also be used.Combinations of crosslinking agents may be used.

The acid generator is preferably an acid generator compound is employedthat liberates acid upon thermal treatment. A variety of known thermalacid generators are suitably employed such as e.g.2,4,4,6-tetrabromocyclohexadienone, benzoin tosylate, 2-nitrobenzyltosylate and other alkyl esters of organic sulfonic acids. Compoundsthat generate a sulfonic acid upon activation are generally suitable.Other suitable thermally activated acid generators are described in U.S.Pat. Nos. 5,886,102 and 5,939,236; the disclosures of these two patentsare incorporated herein by reference. If desired, a radiation-sensitiveacid generator may be employed as an alternative to a thermallyactivated acid generator or in combination with a thermally activatedacid generator. Examples of suitable radiation-sensitive acid generatorsare described in U.S. Pat. Nos. 5,886,102 and 5,939,236. Otherradiation-sensitive acid generators known in the resist art may also beused as long as they are compatible with the other components of theantireflective composition. Where a radiation-sensitive acid generatoris used, the cure (crosslinking) temperature of the composition may bereduced by application of appropriate radiation to induce acidgeneration which in turn catalyzes the crosslinking reaction. Even if aradiation-sensitive acid generator is used, it is preferred to thermallytreat the composition to accelerate the crosslinking process (e.g., forwafers in a production line).

The antireflective compositions of the invention preferably contain (ona solids basis) (i) about 50-98 wt. % of the SiO-containing polymer,more preferably about 70-80 wt. %, (ii) about 1-50 wt. % of crosslinkingcomponent, more preferably about 3-25%, most preferably about 5-25 wt.%, and (iii) about 1-20 wt. % acid generator, more preferably about 1-15wt. %.

The antireflective coating/hardmask compositions of the invention may beused in combination with any desired resist material in the forming of alithographic structure. Preferably, the resist is imageable withultraviolet radiation (e.g.<400 nm wavelength) or with electron beamradiation. Examples of suitable resist materials are described in U.S.Pat. Nos. 5,861,231; 5,962,184; and 6,037,097, the disclosures of whichare incorporated herein by reference.

The antireflective compositions of the invention will typically containa solvent prior to their application to the desired substrate. Thesolvent may be any solvent conventionally used with resists whichotherwise does not have any excessively adverse impact on theperformance of the antireflective composition. Preferred solvents arepropylene glycol monomethyl ether acetate, cyclohexanone, and ethylcellosolve acetate. The amount of solvent in the composition forapplication to a substrate is preferably sufficient to achieve a solidscontent of about 8-20 wt. %. Higher solids content formulations willgenerally yield thicker coating layers. The compositions of theinvention may further contain minor amounts of auxiliary components(e.g., base additives, etc.) as may be known in the art.

The antireflective compositions of the invention can be prepared bycombining the polymer, crosslinking component and acid generator, andany other desired ingredients using conventional methods. Thecompositions of the invention advantageously may be formed intoantireflective layers on a substrate by spin-coating followed by bakingto achieve crosslinking and solvent removal. The baking is preferablyconducted at about 250° C. or less, more preferably about 150°-200° C.,most preferably about 170°-180° C. The baking time may be varieddepending on the layer thickness and bake temperature. A typical time at170° would be about two minutes. The thickness of the antireflectivecomposition of the invention may be varied depending on the desiredfunction. For example, where the composition is used as anon-planarizing antireflective coating, the thickness may be about50-500 nm. Where the composition is used as a planarizing hardmask, thethickness is preferably about 0.5-5.0 μm. If desired, the compositionsof the invention may also be used as dielectric materials in a similarmanner to conventional spin-on glass materials.

The compositions of the invention are especially useful for lithographicprocesses used in the manufacture of integrated circuits onsemiconductor substrates. The compositions are especially useful forlithographic processes using mid-UV, 248 nm deep UV, x-ray, or e-beam orother imaging radiation.

Semiconductor lithographic applications generally involve transfer of apattern to a layer of material on the semiconductor substrate. Thematerial layer of the semiconductor substrate may be a metal conductorlayer, a ceramic insulator layer, a semiconductor layer or othermaterial depending on the stage of the manufacture process and thedesired material set for the end product. The composition of theinvention is preferably applied directly over the material layer to bepatterned, preferably by spin-coating. The composition is then baked toremove solvent and cure (crosslink) the composition. Aradiation-sensitive resist layer can then be applied (directly orindirectly) over the cured antireflective composition of the invention.

Typically, the solvent-containing resist composition is applied usingspin coating or other technique. The substrate with the resist coatingis then preferably heated (pre-exposure baked) to remove the solvent andimprove the coherence of the resist layer. The thickness of the appliedlayer is preferably as thin as possible with the provisos that thethickness is preferably substantially uniform and that the resist layerbe sufficient to withstand subsequent processing (typically reactive ionetching) to transfer the lithographic pattern to the underlyingsubstrate material layer. The pre-exposure bake step is preferablyconducted for about 10 seconds to 15 minutes, more preferably about 15seconds to one minute. The pre-exposure bake temperature may varydepending on the glass transition temperature of the photoresist.

After solvent removal, the resist layer is then patternwise-exposed tothe desired radiation (e.g. 248 nm ultraviolet radiation). Wherescanning particle beams such as electron beam are used, patternwiseexposure may be achieved by scanning the beam across the substrate andselectively applying the beam in the desired pattern. More typically,where wavelike radiation forms such as 248 nm ultraviolet radiation, thepatternwise exposure is conducted through a mask which is placed overthe resist layer. For 248 nm UV radiation, the total exposure energy ispreferably about 100 millijoules/cm² or less, more preferably about 50millijoules/cm² or less (e.g. 15-30 millijoules/cm²).

After the desired patternwise exposure, the resist layer is typicallybaked to further complete the acid-catalyzed reaction and to enhance thecontrast of the exposed pattern. The post-exposure bake is preferablyconducted at about 60-175° C., more preferably about 90-160° C. Thepost-exposure bake is preferably conducted for about 30 seconds to 5minutes.

After post-exposure bake, the resist structure with the desired patternis obtained (developed) by contacting the resist layer with an alkalinesolution which selectively dissolves the areas of the resist which wereexposed to radiation. Preferred alkaline solutions (developers) areaqueous solutions of tetramethyl ammonium hydroxide. The resultinglithographic structure on the substrate is then typically dried toremove any remaining developer solvent.

The pattern from the resist structure may then be transferred to theexposed portions of the layer of antireflective material of theinvention by etching with CF₄ or other suitable etchant using techniquesknown in the art.

After the opening of the layer of antireflective material of theinvention and any underlying antireflective coating, the underlyingmaterial layer to be patterned may then be etched using an etchantappropriate to the material layer composition. Where the material layeris a metal (e.g., Cr) a combination of Cl₂/O₂ may be used as a dryetchant. Once the desired pattern transfer has taken place, anyremaining resist may be removed using conventional stripping techniques.If the composition of the invention is being used strictly as a hardmaskor non-planarizing antireflective coating, the composition of theinvention may be removed by contacting with a CF₄/O₂ plasma.

Thus, the compositions of the invention and resulting lithographicstructures can be used to create patterned material layer structuressuch as metal wiring lines, holes for contacts or vias, insulationsections (e.g., damascene trenches or shallow trench isolation),trenches for capacitor structures, etc. as might be used in the designof integrated circuit devices. The compositions are especially useful inthe context of creating patterned metal structures, especially Cr-basedstructures useful as masks.

Examples of general lithographic processes where the composition of theinvention may be useful are disclosed in U.S. Pat. Nos. 4,855,017;5,362,663; 5,429,710; 5,562,801; 5,618,751; 5,744,376; 5,801,094;5,821,469 and 5,948,570, the disclosures of which patents areincorporated herein by reference. Other examples of pattern transferprocesses are described in Chapters 12 and 13 of “SemiconductorLithography, Principles, Practices, and Materials” by Wayne Moreau,Plenum Press, (1988), the disclosure of which is incorporated herein byreference. It should be understood that the invention is not limited toany specific lithography technique or device structure.

EXAMPLE 1

Ortho Grafting of 9-anthracenemethyl Group toPoly(4-hydroxybenzylsilsesquioxane) and the Formulation ofHardmask/antireflective Layer.

9-anthracene methanol 6.7 g was reacted with 16 g ofpoly(4-hydroxybenzylsilsesquioxane) in 150 g of acetonitrile containing0.4 g of HCl. The solution was heated to reflux for several hours, andthen water was added to precipitate the grafted polymer. The driedpolymer was dissolved as a 14 wt. % solution in propylene glycolmonomethyl ether acetate (PGMEA). Glycoluril resin (POWDERLINKcrosslinking agent) and nitrobenzyl tosylate (acid generator) were addedto the solution in amounts to achieve 10 wt. % of total solids and 5 wt.% of solids respectively. 200 ppm of FC430 surfactant (sold by 3MCorporation) was also added to the solution.

EXAMPLE 2

Etching the Hardmask/antireflective Layer vs. UV-80 with CF₄/O₂ Gas

The hardmask/antireflective layer (HM/ARC), formulated as described inExample 1, was spin-coated on hexamethyldisilazane(HMDS)-primed wafer at3000 rpm. The spun film was cured at 175° C. for 3 minutes. A layer ofUV-80 photoresist (sold by Shipley Company) was spin-coated over thecured layer at 3000 rpm. The photoresist layer was soft baked at 130° C.for 60 seconds.

Thickness measurements were made with a profilometer. To make thethickness measurements, a 13.0 nm Al strip was used as a mask; this Alis not etched in the Cl₂/O₂ or in the CF₄/O₂ plasmas.

A generic oxide etch process was used in the CF₄/O₂ etch with theconditions of Table I. A low pressure, high density plasma process usingan inductively coupled plasma (ICP) was used. Flow rate, pressure, powerand Ar dilution were selected to give a relatively stable processwithout the oscillations frequently encountered with theseelectronegative discharges. The DC self bias voltage was kept to 150volts.

TABLE I Etch condition for CF₄/O₂ CF₄ flow 40 sccm O₂ flow 6 sccm Arflow 25 sccm etch pressure 6.1 mT ICP power 400 W rf substrate power 30W dc bias voltage −150 V

TABLE II Etch thickness and etch rate Etch time 45s 50s 90s UV80 179 nm227 nm  402 nm (4.0 nm/s) (4.5 nm/s)  (4.5 nm/s) HM/ARC 157 nm 205nm >374 nm (3.5 nm/s) (4.1 nm/s) (>4.2 nm/s)

EXAMPLE 3

Etching the Hardmask/antireflective Layer vs. UV80 with Cl₂/O₂ Gas

Both HM/ARC and UV80 were processed as Example 2 except the etchingprocess which is described in Table III.

TABLE III Etch condition for Cl₂/O₂ Cl₂ flow 24 sccm O₂ flow 6 sccm Arflow 25 sccm etch pressure 12 mT ICP power 500 W rf substrate power 12 Wdc bias voltage −114 V

The etch rate of HM/ARC is significantly lower than UV-80.

TABLE IV Etch thickness and etch rate Etch time 50s 150s UV80 61 nm (1.2nm/s) 237 nm (1.5 nm/s) HM/ARC 20 nm (0.4 nm/s)  46 nm (0.3 nm/s)

What is claimed is:
 1. A composition suitable for formation of a spin-onantireflective layer, said composition comprising: (a) a polymercontaining SiO moieties, a plurality of reactive sites distributed alongthe polymer for reaction with a crosslinking component, and chromophoremoieties, (b) a crosslinking component, and (c) an acid generator. 2.The composition of claim 1 wherein said SiO moieties are selected fromthe group consisting of siloxane moieties and silsesquioxane moieties.3. The composition of claim 1 wherein said acid generator is a thermallyactivated acid generator.
 4. The composition of claim 1 wherein saidchromophore moieties are selected from the group consisting ofchrysenes, pyrenes, fluoranthrenes, anthrones, benzophenones,thioxanthones, and anthracenes.
 5. The composition of claim 1 whereinsaid crosslinking component comprises a glycoluril compound.
 6. Thecomposition of claim 1 wherein said composition consists essentially ofcomponents (a), (b), and (c).
 7. The composition of claim 1 wherein saidSiO moieties are in a backbone portion of said polymer.
 8. Thecomposition of claim 1 wherein said composition contains about 50-98 wt.% of (a), about 1-50 wt. % of (b), and about 1-20 wt. % of (c).